(a) Technical Field
The present invention relates to a motor for an environment-friendly vehicle, and more particularly, to a technology associated with a motor for an environment-friendly vehicle that maximizes efficiency regardless of which driving state the vehicle is currently in (i.e., whether the vehicle is traveling at low speeds, medium speeds or high speeds).
(b) Background Art
Generally, a motor is mounted on environment-friendly vehicle (including an electric vehicle, a hybrid electric vehicle, a fuel battery vehicle, and the like) as a power source for providing a drive source to a vehicle. More specifically, an AC electric motor (AC motor) is used to provide this drive force. An AC motor typically includes a stator core 1 wound with a coil that is fixedly installed as illustrated in FIG. 1 and a rotor core 2 is installed in the stator core 1, and a shaft 3 extracting power that is integrally coupled to the rotor core 2. The stator core 1 is often formed by laminating a plurality of thin electrical steel sheets 1a in order to reduce hysteresis loss (iron loss), and insulation coating 1b is applied between the electrical steel sheets 1a for interlayer insulation of the electrical steel sheets 1a. 
In most vehicles, the efficiency of the motor should be maximized at low and medium speeds during which time the frequency use of the motor is quite high. However, it is difficult to increase the motor's efficiency at both low and medium speeds due to the characteristics the currently offered motors.
In conventional motors, a method for increasing efficiency by minimizing the hysteresis loss (iron loss) is often adopted. Advantageously, the thickness of the electrical steel sheet 1a is smaller while the thickness of the insulation coating 1b is larger than conventional designs in order to minimize the hysteresis loss (iron loss) to provide high efficiency at medium and high speeds.
However, when the thickness of the insulation coating 1b is increased, the thickness of the electrical steel sheet 1a which is a pure core serving a movement passage of a magnetic flux is relatively decreased and as a result, output from the motor is decreased (i.e., efficiency is low) at low speeds. As a result, a current value must be increased in order to guarantee the same output at low speeds as medium and high speeds. Unfortunately, however, when the current value is increased, power loss (copper loss) occurs. In other words, in conventional motors, the hysteresis loss (iron loss) is minimized by increasing the thickness of the insulation coating 1b and thus efficiency is increased, and this structure shows high efficiency at medium/high speeds while has having a low efficiency at low speeds.
The thickness of the insulation coating 1b may be decreased in order to increase efficiency at low speeds, but in this case, as the hysteresis loss (iron loss) is increased, the efficiency of the motor overall decreases which is also not ideal. Furthermore, the current value may be increased in order to acquire the same output during low speeds as medium and high speeds, but power loss (copper loss) occurs as a result of this solution. Accordingly, in conventional motors, it is difficult to increase the efficiency at both low speeds and medium/high speeds. Thus, a motor that is able to bridge the gap between the two speed states is needed.
The description provided above as a related art of the present invention is just for helping understanding the background of the present invention and should not be construed as being included in the related art known by those skilled in the art.